(1) Field of the Invention
This invention relates to agricultural irrigation and more particularly to linear systems wherein a pipe is moved transversely of its axis rectalinearly across the field to be irrigated and water dispensed from that pipe.
(2) Description of the Prior Art
The prior Purtell U.S. Pat. No. 4,352,460 (referred to as Purtell No. '460) discloses an automatic irrigation system having an automatic furrow guide. In that system the distance of the pipe from a guide line in the form of a furrow was maintained by changing the angle of the entire elongated pipe. That is to say if the pipe was away from the guide line that the far end of the pipe was made to go faster so that the pipe angled toward the guide line to come nearer to it.
Johnson U.S. Pat. No. 4,172,551 discloses a guide system for a linear move irrigation system.
Purtell U.S. Pat. Nos. 3,245,595 and 3,245,608 (referred to as Purtell No. '595 and '608) discloses an irrigation system wherein the elongated pipe is supported by a plurality of vehicles. The wheels on each vehicle may be steered from right to left. The wheels are hand set to go in one particular direction and locked in that position by a leaf fitting into a notched bar.
Purtell U.S. Pat. No. 3,897,801 (referred to as Purtell No. '801) discloses a system where one or more of the end vehicles supporting an elongated pipe are angled outward so that the end vehicles stretch the entire pipe. The wheels on the vehicle are the same as those disclosed in Purtell Nos. '595 and '608.
Purtell U.S. Pat. No. 3,746,258 (referred to as Purtell No. '258) discloses rotation of a helical tube to move a shaft axially of the tube.
Before this application was filed, a search was made in the U.S. Patent and Trademark Office. That search developed the following patents:
Engel U.S. Pat. No. 2,750,228 PA1 Zimmerer U.S. Pat. No. 3,730,435 PA1 Daugherty U.S. Pat. No. 3,902,668 PA1 Olson U.S. Pat. No. 4,132,244 PA1 Chapman U.S. Pat. No. 4,343,935 PA1 Gheen U.S. Pat. No. 4,350,295